1. Field of the Invention
The present invention relates to cable pulling or winching devices, and to such devices of the type wherein operation of a handle causes separate gripping assemblies to alternately grip, release, move along the cable to re-engage and re-grip the cable. More particularly, the invention relates to such winching devices having means to ensure reliable release of one of the gripping assemblies.
2. Prior Art
A search of the prior art indicates the following U.S. Pat. Nos. may be pertinent to the present invention. U.S. Pat. Nos.:
459,033 Bolon
702,648 Hand
828,820 Lindley
974,258 Green
1,151,670 Donald
1,271,294 Duigan
1,443,064 Wilson
3,341,177 Weise et al.
Devices known as wire stretchers or tensioners are known in art which are used to pull a wire or cable to tension it prior to securing it to a support or to join it to another wire or cable. As used herein, the term "cable" will be used generically to refer to cables, wires or ropes which are used for substantially identical purposes. These wire stretchers generally include two or more cammed gripping elements, at least one of which is movable relative to a support member or the cable being tensioned. The stretcher is secured to a stationary point and the gripping elements are placed on the cable. Back-and-forth operation of a handle or lever causes the movable gripping element to slide along the cable, grip it securely and draw it toward the stationary point, release it, and repeat the process.
Generally, operation of the remaining gripping elements is coordinated to grip the cable when the movable gripping element has released it, and vice-versa, to maintain the cable under tension. In some of the known devices of this type, reliance is place upon the rigidity of the cable to separate the gripping surfaces to permit its passage through the gripping element which has slackened it grip. Devices of this type have been found not to operate reliably in heavy use with small cables or highly-flexible cables which tend to get bent or kinked, and thus jam the gripping elements.
Attempts to overcome these problems have resulted in devices of this type provided with linkages interconnecting the operating handle and the movable gripping surface of each gripping element. Movement of the handle in one direction causes the movable surface to separate from and release the cable in one of the gripping elements, and the movable jaw in the other element to grip the cable and draw it toward the stationary point to which the device is anchored. Movement of the handle in the other direction reverses operation of the gripping elements, and moves one of the gripping elements a distance along the cable for another grip. Usually a spring is provided for each gripping element to ensure that the cable is gripped when the operating handle is not moved.
For various reasons the devices of the prior art have not proven entirely satisfactory. Heretofore, devices of the foregoing type have not been provided with means to ensure that the gripping device which is to release its grip on the cable to permit passage of the cable therethrough, does in fact release its grip. The devices of the prior art have relied upon the interconnecting linkage to displace the cammed gripping surfaces and the stiffness of the length of wire extending between the gripping element, which is generally bowed or otherwise bend into a curved shape, to cause it to pass therethrough. As noted above, this mode of operation is satisfactory only if the cable is sufficiently stiff. Highly flexible cables, or cables of small diameter have not worked satisfactorily with the gripping devices of the foregoing type.
Additionally, since the cable length between the gripping element are bowed, the devices are subject to jamming or failure if the gripping element do not open to permit passage of the wire or cable, and the wire or cable is subjected to undue abrasion and wear, presenting a safety hazard requiring frequent inspection of the device and wire and cable, and more frequent replacement of the cable.